The growth of oxide on initially oxidehyphen;free evaporated aluminum films at room temperature and atmospheric pressure has been studied in parallel experiments, using elliptically polarized light to measure the film thickness and vibrating capacitor measurements to measure changes in the Volta potential. The film thickness reaches 21 Aring; in 106sec and varies essentially logarithmically with time in the time range from 102to 106sec. The Volta potential is almost constant during the initial stages of growth and then varies approximately logarithmically with time. The observed change of Volta potential, interpreted as resulting from changes in the Galvani potential, is approximately 350 mV in 106sec of oxidation.A logical extension of the Mott theory is presented which includes (1) the effect of electronic space charge resulting from equilibration of electrons between the metal and oxide and (2) the electric field in the oxide, both in its role as a barrier to electron penetration of the oxide and in its control over the migration of interstitial aluminum ions. The extended theory predicts a linear relation betweenVfrac12;X(Vis Galvani potential difference across the oxide andXis oxide thickness) and ln (oxidation time) whose slope is 3planck;/(32me)frac12;,mandebeing the mass and charge of the electron andplanck;being Planck's constant divided by 2pgr;. The experimentally determined slope has the value 1.32times;10minus;8Vfrac12;middot;cm as compared to the theoretical slope of 1.46times;10minus;8Vfrac12;middot;cm.
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